1. Field of the Invention
The present invention relates to a method of writing a sequential record, and more particularly to a method of insuring the integrity of data that has been written to a disc medium adopting a fixed-length data recording system.
2. Description of the Related Art
As a method of securely writing data consisting of sequential records to a disc medium, a magnetic disc apparatus employing a variable-length data recording system (referred to as a CKD (Count Key Data) system hereinbelow as an example) has conventionally adopted a method by which data stored in a main memory are divided into blocks in two contiguous data storage areas and the obtained data, having a fixed length and the same content, are written to the above two contiguous data storage area.
FIG. 5 of the accompanying drawings is used for explaining a method of storing data having a variable-length sequential record in a prior art disc medium employing the CKD system. The detail of this method is as follows. For example, as shown in FIG. 5, when updating data 1, data 2, data 3 and data 4 stored in the main memory 31 of the host computer that are sequentially written to the disc medium, which has a data management area 21, data storage areas 22, 23 and 24, and gaps (areas on which no data are recorded) 25, the following steps are performed:
(1) In the first step, a write command is issued twice, and the data 1 are written to two consecutive disc blocks, i.e., the first data storage area 22 and the second data storage area 23; PA1 (2) In the second step, both the data 1 and the data 2 are written in the same manner as in the first step; PA1 (3) In the third step, the data 1, the data 2 and the data 3 are written in the same manner; and PA1 (4) if the data cannot be written in one data area in the fourth step, the area is shifted to the following second data storage area 23 and the following third data storage area 24 and the writing operation is repeated as in the first step.
When a magnetic disc apparatus adopting the CKD system is used, the gap 25 whose length is required for command processing (processing time) exists between the respective data storage areas, and a so-called rotational loss is not hence generated due to the latency of the disc medium, thereby enabling the writing operation.
To guarantee the integrity of the written data, when a failure has occurred during the operation for writing data to, for example, the first data storage area 22, the previously-written data remain in the second data storage area 23; when a failure occurs during the operation for writing information in the second data storage area 23, the previously-written data remain in the first data storage area 22. That is, the integrity of writing operation is guaranteed because data obtained immediately before occurrence of a failure remain on the disc medium.
However, when implementing the method adopted in the conventional CKD system for the magnetic disc apparatus employing the fixed-length data recording system (which will be referred to as an FBA (Fixed Block Architecture) system hereinbelow), for example, when the write command is successively issued twice as described above, since there is no gap whose length is required for command processing (processing time) and the data storage areas are continuously provided on the disc medium, the second write command can be issued only after the recording head has already passed the storage areas in the magnetic disc apparatus of the FBA system. In order to insure that the writing operation is free of any failure during the writing operation, the disc medium must be rotated one more time, and this rotational loss disadvantageously lowers the data transfer efficiency.